Microtome knife



Dec. 28, 1965 R. MARTINELLI 3,225,639

MICROTOME KNIFE Filed Feb. 21, 1964 INVENTOR. ROBERT MARTINELLI HIS ATTORNEY United States Patent 3,225,639 MICRGTOME KNIFE Robert Martinelli, 5938 Walnut St., Pittsburgh, Pa. Filed Feb. 21, 1964, Ser. No. 346,546 2 Claims. (Cl. 83-9155) The present invention relates to microtome knives, and more particularly to an improved microtome knife formed from glass containing manganese oxide.

In preparing biological specimens for electron microscopes, it is essential that very thin sections of tissue can be cut in order to properly examine the specimen. It is often desirable that ultra-thin sections of a thickness on the order of 200 to 500 Angstrom units be cut from biological tissue. Heretofore, it has been difficult, if not impossible, to cut biological specimens into thin sections of a thickness of only 200 to .300 Angstrom units without distorting the specimen through compression of the tissue or scoring of the tissue by imperfect knife edges. The present invention relates to a knife having a perfect knife edge which can cut the most diflicult types of biological specimen tissue into thin sections having a thickness of 200 to 300 Angstrom units. The present invention also enables the operator of a microtome to cut bone tissue to obtain good microscopic evaluation of the tissue.

In preparing specimens for an electron microscope, an instrument known as a microtome is utilized to section the specimen into very thin pieces. In most microtomes utilized for biological purposes, the knife of the microtome is formed from plate or window glass. The plate or window glass is fractured to expose a sharp edge. The biological specimen is usually prepared for sectioning by utilizing osmium tetroxide as a fixative and embedding the specimen in n-butyl methacrylate so that the polymerized plastic provides a solid matrix with the proper degree of hardness for sectioning by a glass knife.

After the biological specimen has been prepared for sectioning, the embedded specimen is secured to the specimen holder of the microtome. The microtome causes the specimen holder to be moved over the knife edge so that very thin sections of the specimen are sliced from the prepared specimen.

Heretofore, in utilizing conventional plate or Window glass for the microtome knives, the knives had to be made by the technician operating the microtome shortly before they were to be used. The microtome technician actually became, for many purposes, a glazier and scored many pieces of plate or window glass and broke the scored glass into knives before obtaining a good knife. It was also desirable that the knife edge would be fresh.

It was found that if knives of conventional window or plate glass were allowed to stand for an extended period of time, the knife edge, through oxidation of the glass, became imperfect and was not usable. Further, it was found that water tended to dissolve the knife edge of ordinary Window or plate glass knives, thereby rendering them unusable. Accordingly, microtome technicians broke their glass knives immediately before use to get a fresh knife edge and had to change knives frequently.

In the present invention, I have surprisingly discovered that a commercially available glass with manganese oxide forming a constituent part thereof produces a knife blade for a microtome far superior to any knife heretofore used. Microtome knives formed according to the present invention permit cutting into very thin sections of tissue without distortion and without leaving knife or score marks on the specimen. The knives of the present invention also produce a sharp knife edge which is not adversely affected by atmospheric conditions or by water and so can be produced as an article of manufacture and sold to microtome technicians to thereby relieve the microtome tech- 3,225,639 Patented Dec. 28, 1965 nician from the duties of breaking and forming his own glass knives.

In some microtomes, diamond knives have been utilized because the glass knives were unsatisfactory. The diamond knives, as can be appreciated, were very expensive, and there was a great deal of difiiculty in attempting to train technicians to utilize the diamond knives. The present invention provides a knife which gives performance superior in many respects to a diamond knife without the attendant expense. Further, the knives of the present invention can be utilized in many applications not suitable for a diamond knife.

Because the knife of the present invention provides an edge which is relatively permanent, and because the knife of the present invention can be manufactured and sold as an article of manufacture so that the microtome technician does not have to devote a great deal of time to preparing a glass knife, a boat can be afiixed to the knife of the present invention so that the knife and the boat, together, can be sold as an article of manufacture. In conventional microtome operation, a boat is afiixed to the knife to retain a quantity of liquid adjacent the knife edge so that as the tissue specimens are cut by the knife edge, they float onto the liquid within the boat.

Heretofore, microtome technicians, after preparing their knives, had to afiix a boat to the knife to receive the specimens before beginning the cutting operation. In the present invention, the boat can be permanently aflixed to the knife by an epoxy resin, or the like, so that there is no leakage of liquid between the boat and the knife itself as often occurs on conventional glass knives.

I have found that I can prepare a very effective microtome knife from a glass which is semi-opaque, black in color, and is sold commercially by Pittsburgh Plate Glass Company under the name Cararra glass. This black Cararra glass differs from ordinary plate or window glass chiefly in the fact that the ingredient batch from which the black Cararra glass is formed contains approximately 4.22% by weight of manganese oxide (Mn O Pittsburgh Plate Glass Company also sells colored glass under the name Cararra. These glasses come in colors ranging from cream through green. The glasses are described in the following United States Patents: 1,956,176 (Cream); 2,224,469 (Opal Base); 2,237,042 (Red or Pink); 2,282,601 (Ivory); 2,394,502 (White); 2,599,349 (Green); 2,683,666 (Ivory); 2,776,900 (Tan); and 2,956,892 (Blue and Gray).

The black Cararra glass which I have found useful for the present invention is a true glass. All of the other Cararra glasses, as set forth above, are not true glasses, but rather are formed from crystalline substances retained within a glass matrix. I have experimented with the colored Cararra glasses. While they form microtome knives which are superior to ordinary plate glass knives for many purposes, the colored Cararra glasses, other than black, produce microtome knives which are inferior to the black Cararra knife. The colored Cararra glasses form a knife edge which is not so perfect as that formed by the black Cararra glass knife and, accordingly, the colored Cararra knives produce score marks in the tissue specimen sections whereas the knives formed of black Cararra glass do not.

With the foregoing considerations in mind, it is an object of the present invention to provide an improved microtome knife.

Another object of the present invention is to provide a microtome knife which can cut biological tissue specimens as thin as 200 to 300 Angstrom units in thickness without distorting the tissue specimens due to compression or without scoring the surface of the specimen.

Another object of the present invention is to provide an improved microtome knife which is the equivalent or superior to a diamond knife without the attendant cost.

Another object of the present invention is to provide a microtome knife which has a relatively permanent knife edge unaffected by atmospheric conditions.

Another object of the present invention is to provide, as an article of manufacture, a microtome knife with a boat aflixed thereto.

These and other objects of this invention will become apparent as this description proceeds in conjunction with the accompanying drawing.

In the drawing:

FIGURE 1 is a schematic representation, not to scale, of a microtome knife and a microtome specimen holder in various positions relative to the knife;

FIGURE 2 is a side elevation of a microtome knife;

FIGURE 3 is an end elevation of a microtome knife;

FIGURE 4 is a microtome knife boat not affixed to the knife; and

FIGURE 5 is a microtome knife with a boat permanently afiixed thereto.

Referring to the drawing, and particularly to FIGURE 1, there is shown a microtome knife having a cutting edge 12 and positioned within a microtome (not shown). The microtome knife 10 has atfixed thereto a boat which is represented by the wall 16b of the boat in section. A specimen holder 14 of the microtome is shown in two positions in FIGURE 1. In the full line position of specimen holder 14, the holder 14 is being moved downwardly over the knife edge 12 of microtome knife 10. As the holder is so moved, a thin section of the specimen is sliced therefrom.

Liquid 18 retained between the boat 16b and the microtome knife 10 presents a liquid surface upon which the thin sections 20 from the specimen holder 14 float after the specimen has been sectioned.

After: the specimen holder 14 finishes its downward stroke as indicated by arrow A, the specimen holder moves horizontally as indicated by arrow B to the position shown in phantom lines at 14b. The stroke represented by arrow A is the specimen cutting stroke, and the stroke represented by arrow B is the withdrawal stroke of the specimen holder 14. The holder 14 then moves vertically as indicated by arrow C which is the repositioning stroke. After the repositioning stroke, the holder 14 is advanced through the advancing stroke represented by arrow D to again be in position to be moved downwardly through the cutting stroke. In FIGURE 1, the holder 14 is shown partially through the cutting stroke A.

FIGURES 2 and 3 show the improved microtome knife of the present invention. The knives 10 are formed from black Cararra glass and have a cutting edge 12. The cutting edge 12 is formed by taking an oblong plate of black Cararra glass and fracturing the plate along edge 22 to form the cutting edge 12. The fractured edge 22 is at approximately a 45 angle to the vertical sides of the microtome knife 10, although the exact angle of the fractured edge is not critical.

In preparing a knife from Cararra glass, the oblong strip of glass is scored along its surface at approximately a 45 angle to the vertical edges. The glass is then gripped on either side of the score mark and a force is exerted to pull the ends on either side of the score mark away from each other. It has been found that a very good knife edge 12 can be formed by so pulling the ends of the glass apart.

In actual practice, only a small portion of the total width of edge 12 actually cuts the specimen at any one time. The knife may be on the order of A to /8 of an inch in thickness and the knife edge will, accordingly, be at least that long. Actually, only a fraction of /32 or less of an inch actually cuts the specimen at any one time. A perfect knife would have an edge which was perfectly horizontal when placed in a microtome. However, since only a small portion of the edge is used at any one time, the knife edge may, in actual practice, be slightly curved or ragged. It is, however, essential that any segment of the knife edge less than fl of an inch in length be perfectly uniform without score marks of any kind. 7

FIGURE 4 shows a boat 16 prior to its installation on a microtome knife. The boat 16 is actually formed of very thin sheet metal although it could be formed of light plastic. The boat 16 has two triangular side walls 16a and a back wall 1612. At the lower end of the boat, the side walls 16a and the back wall 16b fit snugly against the sides and back of the microtome knife as best shown in FIGURE 5.

In FIGURE 5, an article of manufacture of the knife with the boat is shown at 24. In FIGURE 5, the boat 16 has been atfixed to the microtome knife by a small bead of epoxy resin 26 which seals the boat to the knife and permits liquid to be retained within the boat to float the specimen sections.

As previously stated, the knife of the present invention is formed from a glass manufactured and sold by Pittsburgh Plate Glass Company under the name Cararra glass. The glass is semi-opaque and is black in color.

A typical ingredient batch of the glass, prior to fusing, has the following constituents in percent by weight:

Percent Silica (SiO 69.38 Soda (Na O) 13.20 Calcium oxide (CaO) 6.80 Magnesium oxide (MgO) 4.80 Sodium chloride (NaCl) 0.80 Sodium sulphate (Na SO 0.70 Manganese oxide (Mn O -1 4.22 Chromic oxide (Cr O 0.10

The batch of black Cararra glass may vary slightly, but it should contain from 65% to by weight SiO 8% to 18% by weight Na O, 3% to 9% by weight CaO, 3% to 7% by weight MgO, 0.5% to 1.5% by weight NaCl, 0.5% to 1.5% by weight Na SO 3.5% to 5% by weight Mn O and .05% to .15% Cr O The black Cararra glass of which the knife of the present invention is formed may be produced in conventional glass making fashion. Various size pots or crucibles may be employed and the melting temperatures and times will vary according to the amount being formed. Conditions herein recited may be employed to make 8 pounds of glass in a refractory pot in a furnace heated by the controlled combustion of natural gas.

An empty pot is preheated in the furnace at a furnace temperature of about 2200 F. A portion of the mixed I batch is ladled into the preheated pot and the furnace temperature is gradually increased until it reaches approximately 2500 F. in one hour, at which time a second charge of the remaining batch is added to the pot. The pot and its contents are heated for an additional hour and one-half and the furnace temperature is gradually increased to 2650 F. At the end of this time, the glass is formed in a molten condition. The molten glass is then held at a furnace temperature of 2650 F. for one hour to permit the conclusion of the chemical reactions, the exclusion of gases, and the substantial homogenization of the glass.

The refined glass is cooled to approximately 2200 F. and the pot is removed from the furnace. The contents of the pot are poured on a cast iron table where the glass is rolled in the form of a plate. The plate is placed in a kiln and cooled from a temperature of about 1050 F. to 850 F. at a rate of about 4 F. per minute. During this cooling operation, the glass is annealed. After cooling, the glass may be ground and polished.

In summary, it may be stated that microtome knives formed from black Cararra glass which is manufactured according to the foregoing process, or similar glass making processes, produce a keen cutting edge which is superior to ordinary plate glass or window glass knives. The superiority of the Cararra glass knives is very surprising in that many experts in the glass field cannot attribute any hardening factor to the manganese dioxide (Mn O which is the chief constituent by which black Cararra glass differs from ordinary plate glass or window glass. In fact, glass experts indicated to the inventor prior to the invention hereof, that black Cararra glass was not particularly suitable for microtome knives and would offer no advantages over ordinary plate or window glass. The discovery of the present invention is a startling discovery in view of these opinions by experts.

I have also found that water or other liquids utilized in the boat of the knife have no adverse effect on the knife edge of the present invention, as contrasted to the adverse effect on ordinary glass knives. Accordingly, knives of the present invention have a longer useful life than ordinary knives. Further, ordinary glass microtome knives deteriorate and become useless due to the oxidation of the glass at the knife edge under ordinary atmospheric conditions. I have found that knives formed according to the present invention are not adversely aifected even though they are exposed to the atmosphere for periods up to one month. Accordingly, it is possible to manufacture and sell the knives of the present invention, rather than requiring the microtome technician to break his own knives. It is also possible to now manufacture a microtome knife and permanently attach a boat thereto so that the knife and the boat, together, form an article of manufacture which is new to the field.

According to the provisions of the patent statutes, I have explained the principle, preferred construction and mode of operation of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. A tissue cutting knife for a microtome formed from a piece of glass so fractured as to form a sharp cutting edge, said glass being fused from a batch consisting essentially of the following ingredients in percent by weight: to SiO 8% to 18% Na O, 3% to 9% C210, 3% to 7% MgO, .5% to 1.5% NaCl, 5% to 1.5% Na SO 3.5% to 5% Mn O and .O5% to .15% Cr O 2. A tissue cutting knife for a microtome formed from a piece of glass so fractured as to form a sharp cutting edge, said glass being fused from a batch consisting essentially of the following ingredients in percent by weight:

Haanstra, H. B.: Philips Technical Review, vol. 17, No. 6, pages 178-183.

ANDREW R. JUHASZ, Primary Examiner. 

1. A TISSUE CUTTING KNIFE FOR A MICROTOME FORMED FROM A PICE OF GLASS SO FRACTURED AS TO FORM A SHARP CUTTING EDGE, SAID GLASS BEING FUSED FROM A BATCH CONSISTING ESSENTIALLY OF THE FOLLOWING INGREDIENTS IN PERCENT BY WEIGHT: 65% TO 75% SIO2, 8% TO 18% NA2O, 3% TO 9% CAO, 3% TO 7% MGO, .5% TO 1.5% NACL, .5% TO 1.5% NA2SO4, 3.5% TO 5% MN3O4, AND .05% TO .15% CR2O3. 